High-symmetry crystals exhibit isotropic properties. Inducing anisotropy, e.g., by facet selective etching, is considered implausible in face-centered cubic (FCC) metals, particularly gold, which, in addition to being an FCC, is noble. We report for the first time the facet selective etching of Au microcrystals obtained in the form of cuboctahedra and pentagonal rods from the thermolysis of a goldorganic precursor. The selective etching of {111} and {100} facets was achieved using a capping method in which tetraoctylammonium cations selectively cap the {111} facets while Br^– ions protect the {100} facets. The exposed facets are oxidized by O₂/Cl^–, yielding a variety of interesting geometries. The facet selective etching of the Au microcrystallites is governed only by the nature of the facets; the geometry of the microcystallite does not appear to play a significant role. The etched surfaces appear rough, but a closer examination reveals well-defined corrugations that are indexable to high hkl values. Such surfaces exhibit enhanced Raman activity.

Hexagonal and triangular Au microplates extending over an area of ~12, 000 μm² with thickness in the range 30–1000 nm have been synthesized using a single step thermolysis of (AuCl₄)⁻–tetraoctylammonium bromide complex in air. The microplates are self-supporting and can be easily manipulated using a sharp pin, a property which enables them to serve as substrates for living cells. The microplate surface is non-toxic to living cells and can enhance the fluorescence signal from fluorophores residing within the cell by an order of magnitude. In addition, the microplates are smooth and single-crystalline, and ideal as microscopy substrates and molecular electrodes. The growth of the microplates in the initial stages is interesting in that they seem to grow perpendicular to the substrate, as evidenced by in situ microscopy.

A simple, inexpensive direct micromolding method for patterning Au nanocrystal superlattices using a polydimethylsiloxane (PDMS) stamp has been developed. The method involves in situ synthesis of Au(I) dodecanethiolate and its decomposition leading to Au nanocrystals in the microchannels of the stamp which order themselves to form patterned superlattice stripes, in conformity with the stamp geometry. Owing to its insolubility in common solvents, the dodecanethiolate was made by reacting Au(PPh₃)Cl and dodecanethiol in situ inside the microchannels, by injecting first the former solution in toluene at room temperature followed by the thiol solution at 120 ℃. Annealing the reaction mixture at 250 ℃, resulted in formation of nanocrystals (with a mean diameter of 7.5 nm) and hexagonal ordering. By using an external pressure while molding, parallel stripes with sub-100 nm widths were obtained. The choice of parameters such as injection temperature of the thiol and concentrations is shown to be important if an ordered superlattice is to be obtained. In addition, these parameters can be varied as a means to control the nanocrystal size.

Working with a biased atomic force microscope (AFM) tip in the tapping mode under ambient atmosphere, attoliter (10⁻¹⁸ L) water droplet patterns have been generated on a patterned carbonaceous surface. This is essentially electrocondensation of water leading to charged droplets, as evidenced from electrostatic force microscopy measurements. The droplets are unusual in that they exhibit a highly corrugated surface and evaporate rather slowly, taking several tens of minutes.